U.S. patent number 7,851,344 [Application Number 11/520,668] was granted by the patent office on 2010-12-14 for method of producing a substrate having areas of different hydrophilicity and/or oleophilicity on the same surface.
This patent grant is currently assigned to Seiko Epson Corporation. Invention is credited to Thomas Kugler, Shunpu Li, Christopher Newsome, David Russell.
United States Patent |
7,851,344 |
Kugler , et al. |
December 14, 2010 |
Method of producing a substrate having areas of different
hydrophilicity and/or oleophilicity on the same surface
Abstract
The present invention relates to flexible substrates having on
their surface a wetting contrast. The wetting contrast comprises
adjacent areas of different hydrophilicity and/or oleophilicity.
The present invention further relates to methods of production of
such substrates and to methods of producing microelectronic
components wherein electronically functional material is deposited
onto said substrates. According to a first aspect of the present
invention, a method of producing a flexible substrate having a
wetting contrast is provided. The method includes the step of
forming a first area comprising an inorganic material on a flexible
substrate precursor to form a substrate wherein the inorganic
material is at least partially exposed at the substrate surface and
the first area constitutes a pattern on the precursor surface.
Inventors: |
Kugler; Thomas (Cambridge,
GB), Li; Shunpu (Cambridge, GB), Newsome;
Christopher (Cambridge, GB), Russell; David
(Cambridge, GB) |
Assignee: |
Seiko Epson Corporation (Tokyo,
JP)
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Family
ID: |
35249104 |
Appl.
No.: |
11/520,668 |
Filed: |
September 14, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070066078 A1 |
Mar 22, 2007 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11517444 |
Sep 8, 2006 |
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Foreign Application Priority Data
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Sep 20, 2005 [GB] |
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0519185.1 |
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Current U.S.
Class: |
438/599;
257/E21.575 |
Current CPC
Class: |
H01L
51/0097 (20130101); B82Y 20/00 (20130101); B82Y
30/00 (20130101); H05K 3/125 (20130101); H01L
51/0012 (20130101); H01L 51/0004 (20130101); H05K
3/1208 (20130101); H01L 2251/5369 (20130101); H01L
2251/105 (20130101); Y02P 70/521 (20151101); H05K
2203/013 (20130101); Y02P 70/50 (20151101); H05K
2203/1173 (20130101); Y02E 10/549 (20130101); H05K
2203/095 (20130101); H05K 2203/097 (20130101); H05K
1/0393 (20130101) |
Current International
Class: |
H01L
21/44 (20060101) |
Field of
Search: |
;438/99,151,745,725,758,780 ;257/40 ;136/244 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2 391 385 |
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GB |
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A 56-105960 |
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JP |
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JP |
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Jul 2000 |
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JP |
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A-2004-98351 |
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Apr 2004 |
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JP |
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WO 99/57185 |
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WO |
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WO 01/47045 |
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Jun 2001 |
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WO |
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WO 02/073712 |
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WO |
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WO 03/046062 |
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Jun 2003 |
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WO |
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WO 2004/052647 |
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Jun 2004 |
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WO |
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WO 2005/014184 |
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Feb 2005 |
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WO |
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WO 2005/075112 |
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Aug 2005 |
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WO |
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Other References
C Drummon et al., "Van der Waals Interaction, Surface Free
Energies, and Contact Angles: Dispersive Polymers and Liquids,"
Langmuir 1997, 13, 3890-3895. cited by other .
G. Alberti et al., "Wetting of Rough Surfaces: A Homogenization
Approach," Proc. Roy. Soc. London A.,pp. 1-18, Jun. 21, 2004. cited
by other .
A. Synytska et al., "Tuning Wettability by Controlled Roughness and
Surface Modification Using Core-Shell Particles," Polymeric
Materials: Science and Engineering. 90, pp. 624-625, 624, 2004.
cited by other .
C. Lorenz-Haas et al., "Nucleated Dewetting of Thin Polymer Films,"
Applied Physics A, 74 [Supp.], 383-5, 2002. cited by other .
P. Muller-Buschbaum, "Dewetting and Pattern Formation in Thin
Polymer Films as Investigated in Real and Reciprocal Space," J.
Phys.: Condensed Matte, 15, Abstract, 2003. cited by other .
B. Muller, "Impact of Nanometer-Scale Roughness on Contact-Angle
Hysteresis and Globulin Absorption," J. Vac. Sci. Technol. B,
19(5), pp. 1715-1720, Sep./Oct. 2001. cited by other.
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Primary Examiner: Zarneke; David A
Attorney, Agent or Firm: Oliff & Berridge, PLC
Parent Case Text
This is a Continuation of application Ser. No. 11/517,444, filed
Sep. 8, 2006 now abandoned, which in turn is a non-provisional,
which claims the benefit of Great Britain Patent Application No.
0519185.1, filed Sep. 20, 2005. The disclosure of the prior
application is hereby incorporated by reference herein it its
entirety.
Claims
The invention claimed is:
1. The method of producing a microelectronic component, comprising:
(i) producing a flexible substrate or modified substrate having
adjacent areas of different hydrophilicity and/or oleophilicity on
the same surface by a method comprising: (a) forming a layer
comprising an inorganic material on a flexible substrate precursor
so that substantially no inorganic material is present at the
surface, and (b) patternwise treating the precursor comprising the
layer to reveal inorganic material at the surface where the
precursor has been treated; and (ii) depositing a first solution
onto the substrate or modified substrate to form an area comprising
a first electronically functional material, wherein the
microelectronic component is at least one of a light emitting diode
and a thin-film transistor.
2. The method according to claim 1, wherein the microelectronic
component is a thin-film transistor and the first electronically
functional material is a semiconductor material, and the method
further comprises: (iii) prior to depositing the first solution,
depositing a second solution onto the substrate or modified
substrate to form source and drain electrodes so that these
underlie the area comprising the first electronically functional
material; (iv) depositing a third solution onto the semiconductor
material to form an insulating layer; and (v) forming a gate
electrode on the insulator material in appropriate alignment with
the source and drain electrodes.
3. The method according to claim 1, wherein the microelectronic
component is a light emitting diode, and the first electronically
functional material is a semiconductor material which constitutes a
charge injection layer, and the substrate or modified substrate
comprises an anode, the method further comprising: (iii) depositing
a fourth solution onto the first semiconductor material to form an
area comprising a second emissive semiconductor material; and (iv)
forming a cathode on the second semiconductor material.
4. The method according to claim 1, wherein the deposition of the
solutions is carried out by ink-jet printing.
5. The method according to claim 1, which is carried out using
reel-to-reel processing.
6. A method of making a microelectronic component including a
flexible substrate having adjacent areas of different
hydrophilicity and/or oleophilicity, the method comprising: (i)
producing a substrate by a method comprising: coating a flexible
substrate precursor with a polymer layer including a polymer matrix
and inorganic particles; micro-embossing the polymer layer to form
a pattern at a temperature above a glass transition temperature of
the polymer matrix, the polymer layer having a patterned area and a
non-patterned area; oxidizing an entire surface of the polymer
layer to render the entire surface hydrophilic; and providing a
fluoroalkylsilane to the non-patterned area to render a surface of
the non-patterned area hydrophobic and oleophobic; and (ii)
depositing a first solution onto the substrate to form an area
comprising a first electronically functional material, wherein the
microelectronic component is at least one of a light emitting and a
thin-film transistor.
7. The method according to claim 6, wherein the microelectronic
component is a thin-film transistor and the first electronically
functional material is a semiconductor material, and the method
further comprises: (iii) prior to depositing the first solution,
depositing a second solution onto the substrate or modified
substrate to form source and drain electrodes so that these
underlie the area comprising the first electronically functional
material; (iv) depositing a third solution onto the semiconductor
material to form an insulating layer; and (v) forming a gate
electrode on the insulator material in appropriate alignment with
the source and drain electrodes.
8. The method according to claim 6, wherein the microelectronic
component is a light emitting diode, and the first electronically
functional material is a semiconductor material which constitutes a
charge injection layer, and the substrate or modified substrate
comprises an anode, the method further comprising: (iii) depositing
a fourth solution onto the first semiconductor material to form an
area comprising a second emissive semiconductor material; and (iv)
forming a cathode on the second semiconductor material.
9. The method according to claim 6, wherein the deposition of the
solution is carried our by ink-jet printing.
10. The method according to claim 6, which is carried out using
reel-to-reel processing.
11. A method according to claim 6, wherein the flexible substrate
precursor is selected from the group consisting of metal foils and
polymer foils.
12. A method according to claim 11, wherein the polymer foil is
selected from the group consisting of polyimide foils, polyethylene
terephthalate foils, polyethylene naphthalate foils, polycarbonate
foils, polynorbornene foils and polyethersulfone foils.
13. A method according to claim 6, wherein the inorganic particles
are inorganic oxide particles.
14. A method according to claim 13, wherein the inorganic oxide is
selected from the group consisting of silicon dioxide, aluminum
oxide, titanium dioxide, tin oxide, tantalum pentoxide, indium tin
oxide, perovskites and quaternary oxides.
15. A method according to claim 6, wherein the inorganic particles
have an average particles size of less than 5 .mu.m.
16. A method according to claim 6, wherein oxidation is achieved by
a chemical treatment selected from the group consisting of O.sub.2
plasma treatment, ozone/UV treatment and corona discharge treatment
in air.
17. A method according to claim 6, wherein the fluoroalkylsilane is
(heptadecafluorodecyl)-trichlorosilane.
Description
FIELD OF INVENTION
The present invention relates to a method of producing a flexible
substrate having areas of different hydrophilicity and/or
oleophilicity on the same surface. Such substrates have a use for
example in the field of solution processing to form microelectronic
devices.
TECHNICAL BACKGROUND
Electronically functional materials such as conductors,
semiconductors and insulators have many applications in modern
technology. In particular, these materials are useful in the
production of microelectronic components such as transistors (e.g.
thin film transistors (TFTs)) and diodes (e.g. light emitting
diodes (LEDs)). Inorganic materials such as elemental copper,
elemental silicon, and silicon dioxide have traditionally been
employed in the production of these microelectronic components,
whereby they are deposited using physical vapour deposition (PVD)
or chemical vapour deposition (CVD) methods. Recently, newly
developed materials and material formulations with conducting,
semiconducting or insulating properties have become available and
are being adopted in the microelectronic industry.
One such class of electronically functional materials is that of
organic semiconductor materials. Another class is that of inorganic
metal colloid formulations dispersed in liquid solvents. While the
first example is a recently developed class of materials, the
second example uses traditional materials in a recently developed
formulation type. These materials and material formulations are
associated with a number of advantages over the traditional
materials when used for microelectronic device production. One such
advantage is that these materials can be processed in a greater
variety of ways, including solution processing where the material
is dissolved in a solvent or dispersed as a colloid, and the
resulting solution is used to manufacture e.g. microelectronic
components. This is advantageous because solution processing is
very cost-effective. In particular, a significant saving can be
made in terms of start-up costs associated with setting up plants
for producing microelectronic components when compared with e.g.
silicon semiconductor processing facilities where there is a need
for high capital investment in expensive production facilities.
One particularly promising technique for the processing of
semiconductors to form microelectronic components, for example TFTs
and LEDs, is ink-jet printing. This is because ink-jet printing
conveniently allows relatively precise deposition of a
semiconductor solution onto a substrate in an automated manner. It
would be highly desirable to be able to produce microelectronic
semiconductor components on an industrial scale by ink-jet printing
conductor, semiconductor and insulator solutions onto a suitable
substrate.
However, there are fundamental problems in carrying this out in
practice. The key problem is that, in the production of
microelectronic devices, it is generally necessary to produce
high-resolution patterns of the electronically functional materials
on a substrate. At present, ink-jet printing does not allow a high
enough resolution to be achieved to allow the direct printing of
suitable patterns onto a bare substrate. At present, there are two
ways to avoid this problem.
The first way is to use photolithography to remove undesired areas
of a blanket-deposited electronically functional material, very
high-resolution patterns being obtainable by this method. However,
photolithography is a subtractive technology and is expensive both
in terms of initial investment in expensive photolithographic
equipment and in terms of the relatively large number of processing
steps associated with these techniques, energy consumption and
wasted material.
A second way of circumventing the resolution problems associated
with ink-jet printing of patterns of electronically functional
materials on bare substrates is to form a pre-pattern on the
substrate prior to deposition of the electronically functional
material thereon which directs the ink-jet-printed solution onto
specific areas. Generally, this involves treating the substrate to
form a wetting contrast consisting of adjacent areas on the surface
having different hydrophilicity and/or oleophilicity to ensure
different interaction with electronically functional inks
subsequently printed thereon. Thus a substrate can be produced
having ink-receptive areas and ink-repellent areas, so that a
droplet of ink landing on an ink-receptive area of the substrate
would be prevented from spreading onto the adjacent ink repellent
area. Similarly, any droplet of ink landing so that it contacts
both the ink-receptive and ink-repellent areas would be pushed
towards the ink-receptive areas. In this way, the resolution of an
ink-jet printer can be enhanced to allow the required resolution to
produce patterning as required in the production of microelectronic
devices. For this to work effectively, the difference in
hydrophilicity and/or oleophilicity between the two areas of the
substrate should be as large as possible.
At present, this latter technique requiring the establishment of
adjacent ink-receptive areas and ink-repellent areas on a substrate
has only been realised on inorganic substrates such as indium tin
oxide or silicon oxide (glass) plates. Where such a substrate is
used, it is conventional to apply a photo-crosslinkable polymer
(=negative resist) coating (for example polyimide) to an inorganic
oxide plate and then selectively dissolve those parts of the
polymer coating that were protected by a photomask against the
UV-irradiation during a crosslinking step to reveal the underlying
inorganic oxide. Subsequent treatment of the entire substrate with
e.g. a CF.sub.4 plasma leaves the exposed inorganic oxide substrate
hydrophilic but renders the polymer surface hydrophobic and
oleophobic thus establishing a wetting contrast. Subsequent
printing of an aqueous conductor ink onto the exposed glass parts
allow a high resolution pattern to be formed even if the patterning
carried out is required to be of higher resolution than the ink-jet
printing because droplets of aqueous ink falling in part on the
hydrophobic and oleophobic polymer area will be pushed on to the
hydrophilic glass area.
Whilst this method of creating adjacent ink-receptive and
ink-repellent areas on the substrate is generally quite effective
in increasing the resolution obtainable when ink-jet printing a
solution of an electronically functional material, significant
problems are associated with these techniques when carrying them
out on a commercial scale.
In order to reduce production costs, it is desirable to print
microelectronic devices using a so-called reel-to-reel (R2R)
production environment. Here, a substrate is rolled off a first
reel, processed, and then rolled onto a second reel. A precondition
for using such a production method is that the substrate must be
flexible. At present, the flexible substrates of interest are most
often polymer foils. However, none of the flexible substrates which
are currently available are suitable for making substrates with
appropriate wetting contrasts in a commercially viable manner.
It is possible to produce a wetting contrast on a polymer
substrate, for example by exposing one part of the substrate to
O.sub.2 plasma to render it hydrophilic and to expose another part
to CF.sub.4 plasma to render it hydrophobic and oleophobic.
However, CF.sub.4 treatment affects both pristine polymer surfaces
as well as surfaces which have been exposed to O.sub.2 plasma, so
that surface patterns which are to remain hydrophilic after
CF.sub.4 treatment must be protected by a photoresist mask during
the CF.sub.4 plasma treatment. This is not desirable, in part
because this requires two extra processing steps (the application
and removal of the mask) which adds to the production cost, but
mainly because the hydrophilicity of the hydrophilic area is
decreased on removal of the mask due to residual photoresist
material which cannot be removed. An inversion of the order of the
processing steps might in theory alleviate the latter of these
problems, but cannot be realised as photoresist material does not
adhere to a fluorinated surface. Therefore, it is not possible to
produce flexible substrates with a wetting contrast where the
adjacent areas making up the contrast area differ enough in
hydrophilicity and/or oleophilicity for these to be used to good
effect in ink-jet printing solutions of electronically functional
materials onto these to produce microelectronic components.
Accordingly, there is still a need for the realisation of wetting
contrasts on flexible polymer foils to allow an increase in the
resolution of ink-jet printing electronically functional inks onto
such substrates to produce microelectronic devices such as TFTs and
LEDs.
The present inventors set out to provide a commercially useful
method of producing a substrate having an appropriate wetting
contrast wherein the substrate is not limited to being a rigid
substrate formed from an inorganic oxide such as glass or indium
tin oxide, and wherein the above-mentioned problems can be
avoided.
BRIEF DESCRIPTION OF THE PRESENT INVENTION
According to a first aspect of the present invention, there is
provided a method of producing a flexible substrate having a
surface which comprises adjacent areas of different hydrophilicity
and/or oleophilicity, the method comprising the step of:
(ia) forming a first area comprising an inorganic material on a
flexible substrate precursor to form a substrate wherein the
inorganic material is at least partially exposed at the substrate
surface and the first area constitutes a pattern on the
precursor.
According to second aspect of the present invention, there is
provided a method of producing a flexible substrate having a
surface which comprises adjacent areas of different hydrophilicity
and/or oleophilicity, the method comprising the steps of:
(ib) forming a first area comprising an inorganic material on a
flexible substrate precursor by depositing a first composition
thereon wherein the inorganic material is at least partially
exposed at the surface; and
(ic) forming on the first area a pattern of a second composition
comprising a polymer to form a second area having a different
hydrophilicity and/or oleophilicity to the first area.
According to a third aspect of the present invention, there is
provided a method of producing a flexible substrate having a
surface which comprises adjacent areas of different hydrophilicity
and/or oleophilicity, the method comprising the steps of:
(id) providing a flexible substrate precursor comprising an
inorganic material which is at least partially exposed at the
surface; and
(ie) forming on the precursor a pattern of a composition having a
different hydrophilicity and/or oleophilicity to the precursor.
According to a fourth aspect of the present invention, there is
provided a method of producing a flexible substrate having a
surface which comprises adjacent areas of different hydrophilicity
and/or oleophilicity, the method comprising the steps of:
(if) forming a layer comprising an inorganic material on a flexible
substrate precursor so that substantially no inorganic material is
present at the surface; and
(ig) patternwise treating the precursor comprising the layer to
reveal inorganic material at the surface where the precursor has
been treated.
According to a fifth aspect of the present invention, there is
provided a method of producing a modified substrate (A) having a
surface which comprises adjacent areas of different hydrophilicity
and/or oleophilicity, the method comprising the steps of:
(i) producing a substrate by any method defined above, wherein the
substrate surface comprises an area where the inorganic material is
present and an area where a polymer is present; and
(ii) chemically treating the substrate surface to form the modified
substrate (A) wherein the adjacent surface areas of the modified
substrate (A) have a greater difference in hydrophilicity and/or
oleophilicity than the corresponding areas of the substrate prior
to chemical treatment.
According to a sixth aspect of the present invention, there is
provided a method of producing a modified substrate (B) having a
surface which comprises a first area which is hydrophobic and
oleophilic and an adjacent second area which is hydrophobic and
oleophobic, the method comprising the steps of:
(i) producing a substrate or a modified substrate (A) by any method
defined above; wherein the adjacent areas are respectively
hydrophobic and hydrophilic; and
(ii) treating the substrate or modified substrate (A) with a
fluoroalkylsilane.
According to a seventh aspect of the present invention, there is
provided a method of producing a microelectronic component,
comprising the steps of:
(i) producing a substrate or modified substrate (A) or (B) having
adjacent areas of different hydrophilicity and/or oleophilicity on
the same surface by any method defined above; and
(ii) depositing a first solution onto the substrate or modified
substrate (A) or (B) to form an area comprising a first
electronically functional material.
According to an eighth aspect of the present invention, there is
provided a flexible substrate having adjacent areas of different
hydrophilicity and/or oleophilicity on the same surface, the
substrate comprising an inorganic material on at least part of one
or more of its surfaces.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present inventors have investigated possible ways of producing
a flexible substrate on which it is possible to produce wetting
contrasts. Wetting contrasts consist of areas of differing
hydrophilicity and/or oleophilicity. For the purposes of this
invention, hydrophilicity of a surface is measured via its contact
angle with water, whilst oleophilicity is measured via contact
angles with hexane, that is the angle between a given surface and a
droplet of a designated amount of the relevant liquid. Such contact
angle measurements are well-known in the art, and measurements can
be made using e.g. a goniometer (contact angle measuring device) to
measure droplets of 1-5 .mu.l on a surface of interest. Preferably,
the wetting contrast in the substrates of the present invention
have adjacent surface areas whose contact angles with water and/or
hexane differ by more than 60.degree., preferably more than
80.degree. and most preferably more than 100.degree..
For the purposes of the present invention, the word "hydrophilic"
is used to describe surfaces having a contact angle with water of
less than 60.degree.. The phrase "very hydrophilic" is used to
describe surfaces having a contact angle with water of less than
20.degree.. The phrase "super-hydrophilic" is used to describe
surfaces having a contact angle with water of less than
5.degree..
The word "hydrophobic" is used to describe surfaces having a
contact angle with water of more than 60.degree.. The phrase "very
hydrophobic" is used to describe surfaces having a contact angle
with water of more than 90.degree.. The phrase "super-hydrophobic"
is used to describe surfaces having a contact angle with water of
more than 120.degree..
The word "oleophilic" is used to describe surfaces having a contact
angle with hexane of less than 60.degree.. The phrase "very
oleophilic" is used to describe surfaces having a contact angle
with hexane of less than 20.degree.. The phrase "super-oleophilic"
is used to describe surfaces having a contact angle with hexane of
less than 5.degree.. The word "oleophobic" is used to describe
surfaces having a contact angle with hexane of more than
60.degree.. The phrase "very oleophobic" is used to describe
surfaces having a contact angle with hexane of more than
90.degree.. The phrase "super-oleophobic" is used to describe
surfaces having a contact angle with hexane of more than
120.degree..
The research of the present inventors has led them to find that a
convenient way of achieving good wetting contrasts which consist of
adjacent areas of greatly differing hydrophilicity and/or
oleophilicity is to impart glass-like chemical properties to at
least parts of a flexible polymer foil. This allows the chemical
treatment steps known from the processing of conventional rigid
inorganic oxide substrates to increase a wetting contrast to be
used to create areas of different hydrophilicity and/or
oleophilicity also on a flexible substrate. Thus, the present
invention in its simplest form is realised by applying an inorganic
oxide to at least parts of a flexible polymer substrate precursor
in a manner so that the inorganic oxide is securely attached and
can withstand flexing of the underlying substrate precursor. This
can for example be achieved by depositing a thin layer of inorganic
oxide on a substrate precursor, e.g. by vapour deposition or
chemical deposition. Alternatively, it can be achieved by forming a
mixture of inorganic particles and a polymer matrix on the
substrate precursor and then removing the surface polymer (e.g. by
plasma etching) to reveal the underlying inorganic material.
Another way of achieving this is to adhere particulate inorganic
material to the surface of the substrate precursor.
However, the contribution of the present inventors goes beyond
this, in that they have also discovered that, by varying the
concentration of inorganic material exposed at the surface (e.g. by
varying the vol. % in which inorganic particles are comprised in
the polymer matrix where a mixture of inorganic oxide particles and
a polymer matrix is used) it is possible to vary the extent to
which the surface behaves like the polymer and like the inorganic
material in terms of its response to various chemical treatments.
Where the inorganic material is present in a high concentration at
the surface (e.g. corresponding to 40-60 vol. % of inorganic
material in the polymer matrix mixture relative to the total amount
of polymer and inorganic particles where this technique is used),
the surface behaves much like an inorganic surface. Where the
inorganic material is present in a low concentration (e.g.
corresponding to 0-20 vol. % of inorganic material in the polymer
matrix mixture relative to the total amount of polymer and
inorganic particles where this technique is used), the surface
behaves much like a polymer surface. Where the inorganic material
is present in an intermediate amount (e.g. corresponding to 20-40
vol. % of inorganic material in the polymer matrix mixture relative
to the total amount of polymer and inorganic particles where this
technique is used), the surface behaves neither like the polymer or
the inorganic material but rather displays an intermediate
behaviour.
In particular, where a polymer matrix comprising a relatively small
amount of inorganic particles is used, it is possible to control
the chemical behaviour of the surface. The pristine matrix will
have very little inorganic material present at the surface and will
therefore behave chemically much like the polymer alone. Plasma
etching or other treatment to remove surface polymer will reveal
the underlying inorganic material, so that eventually this will
dominate the chemical behaviour of the surface.
In addition to being able to control the behaviour of the inorganic
material-containing surface, it is also possible to select various
different polymeric substrate precursors, which respond differently
to various chemical treatments.
It is also possible to deposit further layers of polymer onto parts
of the inorganic material regions of the substrate or to mask areas
of the substrate before subjecting it to chemical treatment, so
that only selected areas of the substrate are chemically
modified.
Using these techniques, it is possible to produce a substrate which
has a desired wetting contrast.
In Table 1 below, the hydrophilicities and/or oleophilicities of
various substances are set out. Table 1 also indicates the change
in hydrophilicity and/or oleophilicity achievable by various
chemical treatments.
TABLE-US-00001 TABLE 1 CF.sub.4 plasma O.sub.2 plasma Fluoroalkyl-
No treatment treatment treatment silane treatment SiO.sub.2
Hydrophilic Super- Super- Very Hydrophilic Hydrophilic Hydrophobic
(smooth SiO.sub.2 surfaces) or Super- Hydrophobic (rough SiO.sub.2
surfaces) & Oleophobic Polymethyl- Hydrophobic &
Hydrophobic & Very Hydrophilic -- methacrylate Oleophilic
Oleophobic (PMMA) PMMA + SiO.sub.2 Hydrophobic & Hydrophobic
& Very -- (small Oleophilic Oleophobic Hydrophilic amount of
SiO.sub.2 on surface) PMMA + SiO.sub.2 Very Super Super Super-
(large Hydrophobic & Hydrophilic Hydrophilic Hydrophobic &
amount of Oleophilic Oleophobic SiO.sub.2 on surface)
In the following paragraphs, possible substrate precursors,
possible inorganic oxides and other inorganic materials, possible
matrix polymers, possible methods of oxide deposition, substrate
flexibility and various chemical treatments of substrates to
produce various wetting contrasts will be explained in more detail.
Furthermore, the use of the substrates in producing microelectronic
components is discussed. Then, specific embodiments of the present
invention will be described with reference to the drawings, in
which:
FIG. 1. schematically depicts a first method of realising the
method of the present invention;
FIG. 2. schematically depicts a second method of realising the
method of the present invention;
FIG. 3. schematically depicts a third method of realising the
method of the present invention;
FIG. 4. schematically depicts a fourth method of realising the
method of the present invention;
FIG. 5. schematically depicts a fifth method of realising the
method of the present invention; and
FIG. 6. schematically depicts a sixth method of realising the
method of the present invention.
SUBSTRATE, SUBSTRATE PRECURSOR AND MODIFIED SUBSTRATE
In the present invention, the substrate is a product having a
wetting contrast (i.e. two adjacent surface areas which have
different hydrophilicities and/or oleophilicities).
In the context of the present invention, the term "substrate" is
not limited to the actual substrate used for instance in the
production of a semiconductor element. Rather, "substrate" in this
context is intended to encompass any material on which a further
element, e.g. an electronically functional element, is formed which
includes surfaces already coated and/or patterned with e.g.
conductors, semiconductors or insulators as intermediate products
in the fabrication of e.g. electronic devices such as
transistors.
The substrate precursor is a material which can be processed to
form the substrate.
The modified substrate refers to a substrate which has been
chemically treated to increase the difference in hydrophilicity
and/or oleophilicity between the adjacent areas, relative to the
corresponding areas of the untreated substrate.
In order for the substrate or modified substrate to be useful in
reel-to-reel processing, it must be flexible. Therefore, the
substrate precursor must also be flexible. Other than this
requirement, the nature of the substrate precursor is not
important, especially if none of the precursor material is present
on the surface of the substrate or modified substrate. On the other
hand, it may be that the substrate precursor is not entirely
covered in the substrate or modified substrate product, in which
case its chemical nature, and in particular its hydrophilicity
and/or oleophilicity and susceptibility to changes in
hydrophilicity and/or oleophilicity by various chemical treatments
will be important.
Specific examples of substrate precursors which can be used include
metal foils (e.g. aluminium or steel) and polymer foils produced
from polyimide (PI), polyethylene terephthalate (PET), polyethylene
naphthalate (PEN), polycarbonate (PC), polynorbornene (PNB) and
polyethersulfone (PES).
Where it is desired to use a hydrophilic precursor, foils made from
or coated with e.g. a thin metal layer (e.g. aluminium or steel),
regenerated celluloses, polyvinyl alcohol, polyvinylphenol (PVP) or
polyvinylpyrrolidone can be used.
Where it is desired to use a hydrophobic precursor, polymers such
as polyimide (PI), polyethylene terephthalate (PET), polyethylene
naphthalate (PEN), polycarbonate (PC), polynorbornene (PNB) and
polyethersulfone (PES) can be used.
Substrate Flexibility
As discussed above, the substrates, modified substrates and
substrate precursor of the present invention must be flexible. In
the context of the present invention, this means that the substrate
must be rollable so that it can for example be used in reel-to-reel
processing. Therefore, it is preferably possible to roll the
substrate to form a roll having a diameter of 10 meters or less.
More preferably, it is possible to roll the material to form a roll
having a diameter of 5 meters or less, even more preferably 2
meters or less, most preferably 1 meter or less.
Inorganic Materials
In the present invention, it is in principle possible to use any
inorganic material provided that it has appropriate properties for
producing the desired wetting contrast. The inorganic material used
is preferably an inorganic oxide. For the purposes of the present
invention, the term "inorganic oxide" is taken to encompass
non-organic materials which are solid at room temperature and at
ambient pressure and which have an oxygen atom. Thus minerals
containing oxygen atoms are for the purposes of the present
invention classed as inorganic oxides, as are the solid oxides of
metals (e.g. aluminium and titanium) and the solid oxides of
semi-metals (e.g. silicon). Inorganic oxides which can be used
include binary oxides (such as silicon dioxide (SiO.sub.2),
aluminium oxide (Al.sub.2O.sub.3), titanium dioxide (TiO.sub.2),
tin oxide (SnO.sub.2) and tantalum pentoxide (Ta.sub.2O.sub.5)),
ternary oxides (such as indium tin oxide (ITO) and perovskites
(e.g. CaTiO.sub.3 or BaTiO.sub.3)) and quaternary oxides such as
zeolites (M.sup.n+.sub.x/n[(AlO.sub.2).sub.x(SiO.sub.2).sub.y].
MH.sub.2O).
Furthermore, in addition to the above-mentioned oxides, any
material or material combination that turns hydrophilic upon
exposure to O.sub.2 plasma and/or CF.sub.4 plasma (by initial
formation of a fluorine terminated surface that reacts with water
to form a hydroxy-terminated surface) may be used. Specific
examples include elemental metals or semiconductors such as
aluminium, tin, titanium, aluminium-copper alloys, silicon and
germanium; metal chalcogenides such as tin sulphide and tungsten
selenide; metal nitrides such as boron nitride, aluminium nitride,
silicon nitride and titanium nitride; metal phosphides such as
indium phosphide; metal carbides such as tungsten carbide; and
metal silicides such as copper silicide.
Deposition Methods
In the present invention, it is not significant how the inorganic
material is deposited on the surface of the substrate precursor.
Possible methods of deposition include vapour deposition, chemical
deposition and inclusion of particles of inorganic material at the
surface, for example in a polymer matrix. In view of the importance
of the substrate being able to flex without being damaged, it is
generally preferable for the inorganic material to be included as
particles which are present at least on the surface. This can be
achieved for example by distributing inorganic particles throughout
a substrate precursor from which the substrate is then
produced.
Alternatively, the precursor may be coated with a polymer matrix
comprising the inorganic particles, e.g. by spin-coating and
subsequently etching away part of the polymer surface to reveal the
underlying inorganic particles and thus form the substrate. Where
this technique is used, the polymer and inorganic material are
preferably pre-mixed together with a solvent to form a coating
composition. The solvent may be any appropriate solvent, e.g.
butylacetate. Etching of the coated precursor can for example be
achieved by plasma etching. Where this technique is used, the
polymer matrix is preferably chosen from materials already used in
the field of preparing substrates for use in the preparation of
microelectronic components in view of the fact that skilled workers
are already familiar with such materials. Currently used materials
include polyimides (PI), benzocyclobutene (BCB), epoxy-based
negative resists (e.g. SU-8), photo-initiated curing acrylates
(e.g. Delo-photobond), polyacrylates (e.g. polymethylmethacrylate,
PMMA), polymethylglutarimide (PMGI) and polyvinylphenol. The
mixture of the polymer matrix, the inorganic particles and the
solvent may for example be prepared by mechanical mixing or using
ultrasound. Preferably, the inorganic particles constitute 10-70
vol. % of the mixture, more preferably 20-60, most preferably 30-40
vol. % relative to the total amount of polymer and inorganic
particles.
Depending on the details of the method of production of the
substrate, it may in some cases be preferable to use a precursor
obtainable by coating a substrate base with a mixture comprising
only a relatively small amount of inorganic particles, for example
10-30, more preferably 15-25 vol. % relative to the total amount of
polymer and inorganic particles. In other applications it may be
more preferable to use a precursor obtainable by coating a
substrate base with a mixture having a relatively high content of
the inorganic particles, e.g. 40-60 vol. %, more preferably 45-55
vol. % relative to the total amount of polymer and inorganic
particles. As explained above, the concentration of the inorganic
particles in the polymer matrix is one factor which controls the
extent to which a surface behave like a glass surface or like a
polymer surface, the other factor being the extent to which the
polymer is etched away to reveal the underlying inorganic
particles.
Instead of coating the precursor with a polymer matrix comprising
the inorganic particles, it is also possible according to the
present invention to form the inorganic particles in situ. This
could be done for example by depositing on a precursor a substance
in which inorganic particles will be formed, the formation of these
particles being triggered e.g. by the drying process or by exposure
to a particular reagent. This method of producing the substrates
used in the present invention is particularly preferable where it
is intended to deposit the inorganic-particle layer by ink-jet
printing; it is often problematic to ink-jet print ink solutions
which comprise large, micron-sized (75 microns) particles because
this tends to clog the printer head. An example of a system which
would allow the formation of inorganic particles in situ would be
the deposition of a solution of a polymer matrix (e.g. PMMA) and a
compound of the formula Si(OR).sub.4 wherein R is a C.sub.1-C.sub.6
alkyl group such as an ethyl group in a suitable solvent such as
butylacetate. Such a polymer solution comprises no particles as
such, although SiO.sub.2 particles are formed when the polymer and
silicon-compound mixture is exposed to water, e.g. atmospheric
water vapour. Another way of depositing inorganic particles on a
precursor is to distribute a particulate inorganic material onto an
adherent precursor surface, for example by applying adhesive and
then the inorganic material to the surface, or by heating the
precursor surface to melt it and then distributing inorganic
particles onto the molten surface so that the particles become
fixed thereto on cooling.
It is generally preferable to use an inorganic material in the
particulate form, not only because the resulting substrates are
more robust and less prone to breaking when flexed, but also
because this allows control of the concentration of the inorganic
material on the surface, which allows control of the chemical
properties of the surface layer. Furthermore, the use of
particulate inorganic material is preferable because it increases
the surface area of the substrate surface by making it rougher.
This affects the surface properties of the substrate, increasing a
substrate's philicity or phobicity to a particular solvent. Thus,
roughening a surface renders a hydrophilic surface more
hydrophilic, a hydrophobic surface more hydrophobic, an oleophilic
surface more oleophilic, and an oleophobic surface more oleophobic.
This is useful when producing substrates with wetting contrasts
whose areas differ greatly in hydrophilicity and/or
oleophilicity.
When using particulate inorganic materials, the particles
preferably have an average particle size as measured by
Transmission Electron Microscopy (TEM) of less than 5 .mu.m, more
preferably less than 0.5 .mu.m, most preferably less than 0.05
.mu.m. The particles are preferably nanoparticles having an average
size in the range 5-1000 nm, more preferably 5-100 nm, most
preferably 10-20 mm. Such small particles are preferable for a
number of reasons:
Firstly, small particles result in better optical quality of the
resulting substrates. For particle sizes smaller than the
wavelength of the visible light, light scattering is avoided and a
clear particle-polymer composite film can be obtained. This is
important where the substrate is used in display applications.
Secondly, small particles result in an appropriate roughness of the
surface layer. Nanoparticles are preferable to micron-sized
particles, as the latter result in a surface roughness of the
composite film on a scale corresponding to the particle sizes.
Although it is generally preferable for a substrate to have a rough
surface for the reasons discussed above, there is a limit to how
rough a surface can be and still allow appropriate end products
(e.g. microelectronic components) to be produced. Substrates for
microelectronic applications should have a surface roughness below
the required pattern sizes. Therefore, the use of nanoparticles
allows the surface area of the substrate surface to be increased
without roughening the surface to the extent that further
processing becomes difficult.
Thirdly, small particles are preferably used in view of the
chemical homogeneity of the substrate. In order to achieve
high-resolution patterning by ink-jet printing, the lateral
variations in the surface composition, which result in a
corresponding variation of the surface energy, should preferably be
on a scale smaller than the required pattern sizes.
Chemical Treatments
When substrates of the present invention are subjected to various
chemical treatments, it is possible to change the hydrophilicities
and/or oleophilicities of the various materials present at the
surface. This allows a substrate to be modified so that an
appropriate wetting contrast is available for the intended use.
Whilst many types of chemical treatment could in principle be used,
only the following three types of treatment are discussed in
detail: (i) fluorination treatment, (ii) oxidation treatment and
(iii) fluoroalkylsilane treatment.
(i) Fluorination Treatment
Fluorination of a surface is achieved by chemical treatment, for
example with SF.sub.6 or CF.sub.4 plasma.
Treatment by exposure of a surface to CF.sub.4 plasma fluorinates
even relatively unreactive moieties on that surface. Thus, for
example, where an alkyl moiety is present on the surface, it will
become fluorinated. As fluorocarbon moieties are hydrophobic and
oleophobic, fluorination of common polymer materials such as
polymethylmethacrylate (PMMA), polyimide (PI) and polyethylene
terephthalate (PET) will render them hydrophobic and
oleophobic.
In contrast, fluorination of an inorganic surface will result in
the formation of the corresponding inorganic fluorides, which are
most often reactive towards nucleophiles such as water molecules
and form a hydrophilic hydroxyl-terminated surface upon exposure to
water. For example, fluorination of SiO.sub.2 results in the
formation of Si--F bonds. Si--F bonds are relatively unstable, and
are converted to Si--OH groups when exposed to moist air or
water.
Where a polymer matrix comprising an inorganic material is exposed
to CF.sub.4 plasma, the concentration of inorganic particles at the
surface is important in determining whether the surface is rendered
hydrophilic or hydrophobic and oleophobic. A large concentration of
inorganic particles at the surface will make the material behave
more like the inorganic material and less like the matrix material,
yielding a hydrophilic surface on fluorination. In contrast, where
only a low surface concentration of the inorganic particles is
present, the material will act more like the matrix polymer and
will yield a hydrophobic and oleophobic surface upon fluorination.
Prolonged exposure of a low concentration matrix of inorganic
particles to CF.sub.4 plasma will tend to make the surface more
hydrophilic, as the matrix material becomes etched away by the
plasma revealing a greater surface area of the inorganic particles.
Treatment of hydroxylated groups with CF.sub.4 plasma effectively
replaces the --OH moieties with --F moieties, probably by etching
away the surface layer containing the OH-bonds and providing a
newly formed surface which is F-terminated. Whilst CF.sub.4 plasma
treatment is often used in laboratory scale production of wetting
contrasts on inorganic substrates, it is preferable not to use such
steps in commercial manufacture of these as a vacuum chamber is
required to carry out plasma treatment. This is generally not
practical in a factory setting, and adds expenditure.
(ii) Oxidation Treatment
Oxidation of a surface is achieved by chemical treatment, for
example with O.sub.2 plasma, ozone/UV or by corona discharge
treatment in air.
Treatment by exposure of a surface to O.sub.2 plasma oxidises even
relatively unreactive moieties on that surface. Thus, for example,
where an alkyl moiety is present on the surface, it will become
oxidised, forming hydroxyl, carbonyl, and carboxylic acid groups.
As hydroxyl and carboxylic acid moieties are hydrophilic, oxidation
of common polymer materials such as polymethylmethacrylate (PMMA),
polyimide (PI), and polyethylene terephthalate (PET), will render
them hydrophilic.
Exposure of an inorganic material to O.sub.2 plasma similarly
introduces hydrophilic hydroxyl groups after exposure to
atmospheric moisture or water.
Thus, oxidation treatment, e.g. by exposure to O.sub.2 plasma,
renders both inorganic materials and polymers hydrophilic. It
follows that also exposure to a surface comprising an inorganic
material and a matrix polymer results in a hydrophilic surface,
regardless of the surface concentration of the inorganic material.
Whilst O.sub.2 plasma treatment is often used in laboratory scale
production of wetting contrasts, it is preferable not to use such
steps in commercial manufacture of these as a vacuum chamber is
required to carry out plasma treatment. This is generally not
practical in a factory setting, and adds expenditure. Alternatives
include UV-ozone or corona (electrical discharge) treatments.
(iii) Fluoroalkylsilane Treatment
Treatment of a surface, for example by exposure to a material such
as (heptadecafluorodecyl)-trichlorosilane
(CF.sub.3(CF.sub.2).sub.7CH.sub.2CH.sub.2SiCl.sub.3) in hexane
results in the grafting of fluoroalkylsilane molecules onto
reactive moieties on the surface such as hydroxyl groups. Thus
fluoroalkylsilane molecules become grafted to the surface oxygen
atoms of an inorganic surface treated with e.g.
(heptadecafluorodecyl)-trichlorosilane
(CF.sub.3(CF.sub.2).sub.7CH.sub.2CH.sub.2SiCl.sub.3) in hexane.
This renders the surface super-hydrophobic and oleophobic. Where an
inorganic material has no moieties which are reactive towards
fluoroalkylsilanes, an oxidation treatment may be required before
exposure to the fluoroalkysilane.
Exposure of a pristine polymer to a fluoroalkylsilane treatment has
no effect, as C--H bonds are not reactive towards trichlorosilanes
under the reaction conditions usually applied for silanisations. It
is possible to graft fluoroalkylsilanes to an oxidised polymer that
contains hydroxyl moieties, for example a polymer oxidised by
exposure to O.sub.2 plasma. However, the C--O--Si bonds which are
formed are easily cleaved by hydrolysis or reaction with other
nucleophiles. For this reason, a fluoroalkylsilane treatment is
generally not used to render polymer surfaces hydrophobic and
oleophobic and their use is in practice restricted to the
modification of inorganic oxide substrates.
The effect of silanisation with a fluoroalkylsilane of a polymer
matrix comprising inorganic particles depends on the concentration
of inorganic hydroxyl groups at the surface. Where the
concentration is high, the surface is rendered super-hydrophobic
and oleophobic. The less inorganic hydroxyl groups there are
present at the surface, the less this is observed.
Producing Flexible Substrates Having Hydrophilic vs. Hydrophobic
and Oleophobic Wetting Contrasts
The present invention provides several specific ways in which
flexible substrates having hydrophilic vs. hydrophobic/oleophobic
wetting contrasts can be produced.
According to a first method depicted schematically in FIG. 1, a
flexible substrate having a hydrophilic vs. hydrophobic and
oleophobic wetting contrast is prepared by coating a flexible
polymer substrate precursor (1) (e.g. a polyimide (PI),
polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
polycarbonate (PC), polynorbornene (PNB) or polyethersulfone (PES)
sheet with e.g. a thickness of 100-150 .mu.m and A4 (210.times.297
mm) dimensions) with a composition comprising a polymer (2) (e.g.
polymethylmethacrylate (PMMA)), particles (e.g. nanoparticles of
average particle size 10-20 nm) of an inorganic material (e.g.
SiO.sub.2) and a solvent (e.g. butylacetate) (Step A). The
inorganic material may for example be present in an amount of 20
vol. % relative to the total amount of polymer and inorganic
particles. For example, a 1 .mu.m thick layer of polymer matrix and
inorganic particles could be applied to the substrate precursor by
spin-coating or doctor-blading. The coated substrate precursor is
then left to dry, to form the substrate.
Subsequently, the substrate is coated with a photoresist material
(3) (e.g. by spin-coating a Shipley photoresist S1800 series) (Step
B) which is then removed in a pattern as desired (e.g. using UV
exposure through a photomask, followed by a photoresist development
with MF 319 developer) to reveal a pattern of the underlying
polymer and inorganic material layer (Step C). Then, the surface is
exposed to a prolonged surface oxidation treatment (e.g. by O.sub.2
plasma for 20 seconds at a flow-rate of 200 ml/min and at a power
of 200 W) which strips away a portion of the polymer matrix
surrounding the inorganic particles, thus revealing the inorganic
particles at the surface and rendering the treated part of the
surface hydrophilic (Step D). Next, the photoresist (3) is removed
(e.g. by Microposit remover 1165) (Step E). In a final step (Step
F), the entire surface of the substrate is exposed to a short
CF.sub.4 plasma treatment (e.g. 7 seconds at a flow-rate of 200
ml/min and at a power of 200 W), which retains the hydrophilicity
of the patterned areas which are high in surface inorganic material
concentration and renders the unpatterned areas which are low in
surface inorganic material concentration hydrophobic and
oleophobic.
According to a second method, depicted schematically in FIG. 2, a
flexible substrate having a hydrophilic vs. hydrophobic and
oleophobic wetting contrast is prepared by coating a flexible
polymer substrate precursor (1) (e.g. a polyimide (PI),
polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
polycarbonate (PC), polynorbornene (PNB) or polyethersulfone (PES)
sheet with e.g. a thickness of 100-150 .mu.m and A4 (210.times.297
mm) dimensions) with a composition comprising a polymer (2) (e.g.
PMMA), particles (e.g. nanoparticles of average particle size 10-20
nm) of an inorganic material (e.g. SiO.sub.2) and a solvent (e.g.
butylacetate) (Step A). The inorganic material may for example be
present in an amount of 50 vol. % relative to the total amount of
polymer and inorganic particles. For example, a 1 .mu.m thick layer
of polymer matrix and inorganic particles could be applied to the
substrate precursor by spin-coating or doctor-blading. The coated
substrate precursor is then left to dry, to form the substrate.
The substrate is coated with a polymer (4) (e.g.
polyvinylpyrrolidone) comprising a crosslinker (e.g. a UV
crosslinker such as divinylbenzene) (Step B). The polymer coating
may be applied in a thickness of e.g. 2 .mu.m, and the crosslinker
may be comprised in an amount of e.g. 2-5 wt. %. The polymer
coating is then selectively exposed to crosslinking conditions
(e.g. UV light where a UV crosslinker is used) in a patterned area
(Step C) The surface is then washed with an appropriate solvent
(e.g. water where a polyvinylpyrrolidone polymer is used) to remove
to the polymer (4) from areas which were not crosslinked (Step D).
The underlying polymer (2) and inorganic material layer will thus
be exposed in these areas. Subsequently, the surface is fluorinated
(e.g. by exposure to CF.sub.4 plasma for 7 seconds at a flow-rate
of 200 ml/min and at a power of 200 W), which renders the
crosslinked polymer areas (4) hydrophobic/oleophobic and renders
the polymer (2) and inorganic material layer hydrophilic (Step
E).
According to a third method, depicted schematically in FIG. 3, a
flexible substrate having a hydrophilic vs. hydrophobic and
oleophobic wetting contrast is prepared by coating a flexible
polymer substrate precursor (1) (e.g. a polyimide (PI),
polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
polycarbonate (PC), polynorbornene (PNB) or polyethersulfone (PES)
sheet with e.g. a thickness of 100-150 .mu.m and A4 (210.times.297
mm) dimensions) with a composition comprising a photocrosslinkable
polymer (2) (e.g. polystyrene), particles (e.g. nanoparticles of
average particle size 10-20 nm) of an inorganic material (e.g.
SiO.sub.2), a crosslinker (e.g. a UV crosslinker such as
divinylbenzene) and a solvent (e.g. butylacetate) (Step A). The
inorganic material may for example be present in an amount of e.g.
50 vol. % relative to the total amount of polymer and inorganic
particles. The crosslinker may for example be present in an amount
of e.g. 5 wt. % of the composition. For example, a 2 .mu.m thick
layer of polymer matrix and inorganic material could be applied to
the substrate precursor by spin-coating or doctor-blading. The
coated substrate precursor is then left to dry, to form the
substrate.
The substrate is then selectively exposed to crosslinking
conditions (e.g. UV light where a UV crosslinker is used) in a
patterned area (Step B). The surface is then washed with an
appropriate solvent (e.g. mesitylene where polystyrene is used) to
remove to the polymer (2) and inorganic material from areas which
were not crosslinked, to reveal the underlying polymer substrate
precursor (1) (Step C). Subsequent treatment of the surface with
CF.sub.4 plasma (e.g. by exposure to CF.sub.4 plasma for 7 seconds
at a flow-rate of 200 ml/min and at a power of 200 W) renders the
polymer precursor areas (1) hydrophobic and oleophobic, but removes
the top layer of polymer from the inorganic material-containing
polymer (2) layer to reveal the inorganic particles at the surface
and render it hydrophilic (Step D).
According to a fourth method, depicted schematically in FIG. 4, a
flexible substrate is prepared by coating a flexible polymer
substrate precursor (1) (e.g. a polyimide (PI), polyethylene
terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate
(PC), polynorbornene (PNB) or polyethersulfone (PES) sheet with
e.g. a thickness of 100-150 .mu.m and A4 (210.times.297 mm)
dimensions) with a composition comprising a polymer (2) (e.g.
PMMA), particles (e.g. nanoparticles of average particle size 10-20
nm) of an inorganic material (e.g. SiO.sub.2) and a solvent (e.g.
butylacetate) (Step A). The inorganic material may for example be
present in an amount of 50 vol. %. For example, a 2 .mu.m thick
layer of polymer matrix and inorganic material could be applied to
the substrate precursor by spin-coating or doctor-blading. The
coated substrate precursor is then left to dry, to form the
substrate.
The substrate is then micro-embossed to form a patterned area where
the polymer layer (2) is compressed (Step B). This can for example
be achieved using a hard stamp at a temperature above the glass
transition temperature of the matrix polymer. The surface is then
oxidised (e.g. by exposure to O.sub.2 plasma for 7 seconds at a
flow-rate of 200 ml/min and at a power of 200 W) to render the
entire surface hydrophilic (Step C). A fluoroalkylsilane (e.g.
heptadecafluorodecyl)-trichlorosilane) is then applied to the
surface areas which were not embossed, by application e.g. via a
non-patterned (flat) polydimethylsiloxane (PDMS) stamp (Step D).
This renders the unembossed (surface) areas hydrophobic and
oleophobic.
According to a fifth method, depicted schematically in FIG. 5, a
flexible substrate having a hydrophilic vs. hydrophobic and
oleophobic wetting contrast is prepared by coating a flexible
polymer substrate precursor (1) (e.g. a polyimide (PI),
polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
polycarbonate (PC), polynorbornene (PNB) or polyethersulfone (PES)
sheet with e.g. a thickness of 100-150 .mu.m and A4 (210.times.297
mm) dimensions) with a composition comprising a polymer (2) (e.g.
PMMA), particles (e.g. nanoparticles of average particle size 10-20
nm) of an inorganic material (e.g. SiO.sub.2) and a solvent (e.g.
butylacetate) (Step A). The inorganic material may for example be
present in an amount of 50 vol. % relative to the total amount of
polymer and inorganic particles. For example, a 2 .mu.m thick layer
of polymer matrix & inorganic material could be applied to the
substrate precursor by spin-coating or doctor-blading. The coated
substrate precursor is then left to dry, to form the substrate.
The substrate is then micro-embossed (e.g. using a hard stamp at a
temperature above the glass transition temperature of the matrix
polymer) to form a patterned area where the polymer layer (2) is
compressed (Step B). The surface is then oxidised (e.g. by exposure
to O.sub.2 plasma for 7 seconds at a flow-rate of 200 ml/min and at
a power of 200 W) to render the entire surface hydrophilic (Step
C). Then, the polymer (2) and inorganic material layer is removed
from the embossed areas (e.g. by de-scumming treatment with a mixed
O.sub.2/CF.sub.4 plasma for 1 minute at a flow-rate of 200 ml/min
and at a power of 200 W) to expose the precursor in the embossed
areas (Step D). Subsequent exposure of the surface to CF.sub.4
plasma renders the exposed precursor hydrophobic and oleophobic,
while the non-embossed areas are rendered hydrophilic (Step E).
Producing Substrates Having Hydrophilic vs. Hydrophobic and
Oleophilic Wetting Contrasts
According to a sixth method depicted schematically in FIG. 6, a
substrate having hydrophilic vs. hydrophobic and oleophilic wetting
contrasts is prepared by coating a substrate base (1) (e.g. a
polyimide (PI), polyethylene terephthalate (PET), polyethylene
naphthalate (PEN), polycarbonate (PC), polynorbornene (PNB) or
polyethersulfone (PES) sheet with e.g. a thickness of 100-150 .mu.m
and A4 (210.times.297 mm) dimensions) with a composition comprising
a polymer (2) (e.g. polymethylmethacrylate (PMMA)), particles (e.g.
nanoparticles of average particle size 10-20 nm) of an inorganic
material (e.g. SiO.sub.2) and a solvent (e.g. butylacetate) (Step
A). The inorganic material may for example be present in the
polymer in an amount of 50 vol. % relative to the total amount of
polymer and inorganic particles. For example, a 1 .mu.m thick layer
of polymer matrix and inorganic material could be applied to the
substrate base by spin-coating or doctor-blading. The coated
substrate base is then left to dry, to form a substrate
precursor.
Subsequently, the substrate precursor is coated with a photoresist
material (3) (e.g. Shipley photoresist S1800 series) (Step B) which
is then removed in a pattern as desired using e.g. UV exposure
through a photomask, followed by a photoresist development with MF
319 developer) to reveal a pattern of the underlying polymer and
inorganic material layer (Step C). Then, the surface is exposed to
a surface oxidation treatment (e.g. by O.sub.2 plasma for 7 seconds
at a flow-rate of 200 ml/min and at a power of 200 W) which etches
away a portion of the polymer matrix surrounding the inorganic
particles, thus revealing the inorganic material at the surface and
rendering the treated part of the surface hydrophilic (Step D).
Next, the photoresist (3) is removed (e.g. by Microposit remover
1165) (Step E) to form the substrate.
The resulting substrate has a good wetting contrast formed between
the etched and unetched areas of the surface layer of the substrate
wherein the difference in hydrophilicity and/or oleophilicity
between these areas is greater than that which is achievable in the
prior art (when avoiding fluorinated surfaces), in part because of
the surface roughening caused both in the etched and unetched areas
as a result of the presence of the inorganic particles both on and
immediately under the surface of the substrate. This is useful in
certain applications where it is not desirable to use substrates
with fluorinated surfaces.
Methods of Producing Microelectronic Components
The most important use of the substrates obtainable by the methods
of the present invention and the substrates of the present
invention is in the production of microelectronic components by
ink-jet printing or otherwise depositing electronically functional
inks onto the substrates. In particular, microelectronic components
such as thin-film transistors and light-emitting diodes can be
produced by appropriate sequential deposition of electronically
functional ink onto the substrates, the wetting contrasts helping
to direct the electronically functional inks onto appropriate areas
of the substrate. In these processes, it is not necessarily the
case that all of the elements which make up the microelectronic
component are ink-jet printed. It may be the case that some or all
of the elements are deposited by other means. However, it is most
preferable to use ink-jet printing to deposit all of the elements
making up the microelectronic component on the substrate. It is
particularly preferable to deposit any semiconductor layers using
ink-jet printing.
For example, the substrates of the present invention could be used
to produce a thin-film transistor by ink-jet printing (or otherwise
depositing) a conductor solution onto the substrate to form source
and drain electrodes, making use of the wetting contrasts to
deposit the electrodes accurately. After the conductor ink has
dried to form the electrodes, a solution comprising a semiconductor
is deposited (e.g. by ink-jet printing) onto the substrate with the
electrodes and left to dry. An insulator material is then deposited
onto the dried semiconductor material (e.g. by ink-jet printing).
Once the insulator material is dry, a gate electrode is formed on
the insulator material in appropriate alignment with the source and
drain electrodes, thus completing the formation of the thin-film
transistor.
The substrates of the present invention can also be used to produce
for example a light-emitting diode. This is achieved by firstly
ink-jet printing or otherwise depositing a semiconductor material
onto a substrate on which an electrode has already been formed
(e.g. by ink-jet printing a conductor solution onto the substrate),
again making use of the wetting contrast, and leaving the deposited
ink to dry to form a charge injection layer. Once the charge
injection layer is dry, an emissive semiconductor material is
deposited onto the charge injection layer (e.g. by ink-jet
printing). Once this is dry, a cathode is formed on the emissive
semiconductor material.
EXAMPLES
The following experimental work was carried out by the present
inventors, and supports their findings that flexible substrates
comprising wetting contrasts associated with inorganic materials at
their surfaces are advantageous in that adjacent surface areas
differing greatly in hydrophilicity and/or oleophilicity can be
achieved. It is noted that although rigid glass plates were used in
the Examples, the techniques shown are equally applicable to
flexible substrate precursors in which case flexible substrates
with good wetting contrasts would be produced.
Example 1
Modification of Surface Properties by Plasma Treatment
Preparation of Substrates
Reference Substrate
A 3% polymethylmethacrylate (PMMA) solution in butylacetate was
prepared by dissolving 0.93 g of PMMA (from Sigma Aldrich) in 30 ml
butylacetate. 0.5 ml of the solution was spin coated onto a glass
substrate (12.times.12 mm) precursor (7059 from Corning) for 30
seconds at 1500 rpm in air. The coated precursor was then annealed
for 10 minutes at 100.degree. C. in air to form a Reference
Substrate.
Substrate 1
0.028 g of nanoparticulate SiO.sub.2 (hexamethyldisilazane treated
silica particles, 10-20 nm, from ABCR) was dispersed in 1 ml 6%
PMMA in butylacetate (Aldrich) and 1 ml butylacetate (Aldrich). The
mixture was mixed thoroughly by stirring on a magnetic stirrer and
by a final ultrasonic mixing step in an ultrasonic bath for 5
minutes to yield a solution comprising 17.3 vol. % SiO.sub.2. 0.5
ml of the solution was spin coated onto a glass substrate precursor
(12.times.12 mm plate, 7059 from Corning) for 30 seconds at 1600
rpm in air. The coated precursor was then annealed for 12 minutes
at 100.degree. C. in air to form Substrate 1.
Substrate 2
The procedure outlined above for substrate 1 was repeated, except
that 0.056 g of SiO.sub.2 was used. The solution thus obtained
comprised 29.5 vol. % SiO.sub.2. The solution was spin-coated onto
a precursor as in Example 1, except that it was carried out at 2000
rpm.
Substrate 3
The procedure outlined above for substrate 1 was repeated, except
that 0.085 g of SiO.sub.2 was used and that 1.5 ml of butylacetate
was used rather than 1 ml. The solution thus obtained comprised
38.6 vol. % SiO.sub.2. The solution was spin-coated onto a
precursor as in Example 1, except that it was carried out at 2000
rpm.
Substrate 4
The procedure outlined above for substrate 1 was repeated, except
that 0.110 g of SiO.sub.2 was used and that 2 ml of butylacetate
was used rather than 1 ml. The solution thus obtained comprised
44.9 vol. % SiO.sub.2. The solution was spin-coated onto a
precursor as in Example 1, except that it was carried out at 2000
rpm.
Substrate 5
The procedure outlined above for substrate 1 was repeated, except
that 0.136 g of SiO.sub.2 was used and that 2 ml of butylacetate
was used rather than 1 ml. The solution thus obtained comprised
50.4 vol. % SiO.sub.2. The solution was spin-coated onto a
precursor as in Example 1, except that it was carried out at 2000
rpm.
Plasma Treatment and Measurements
Substrates 1-5 and the Reference Substrate were rinsed with water.
Then the contact angles with water droplets of size 1-5 .mu.l were
measured for each of these six substrates using a goniometer
(=contact angle measuring device).
Subsequently, each of the six substrates was exposed to an O.sub.2
plasma treatment (in a Branson/IPC Series S2100 Plasma Stripper
system equipment) for 7 seconds at a flow rate of 200 ml/min and at
a power of 200 W. Contact angles of the treated substrates were
measured using the same apparatus and methods as above.
Subsequently, each of the six oxidised substrates was exposed to
CF.sub.4 plasma in a Branson/IPC Series S2100 Plasma Stripper
system for 7 seconds at a flow rate of 200 ml/min and at a power of
200 W. Then the substrates were rinsed with de-ionised water (Elix
10 DI water plant). Contact angles of the treated substrates were
measured using the same apparatus and methods as above.
Finally, the film thickness of each of the six substrates was
measured using a Dektak 8 stylus profiler technique.
The resulting data is set out in table 2 below:
TABLE-US-00002 TABLE 2 Ref. B1 B2 B3 B4 B5 Vol. % (SiO.sub.2) in
solid film 0 17.3 29.5 38.6 44.9 50.4 Spin-coating speed (rpm) 1500
1600 2000 2000 2000 2000 I. Initial contact angle 74.degree. 82
92.degree. 100.degree. 117.degree. 125.degree. after water-rinse
II. Contact angle after 7.degree. 15.degree. 5.degree. 5.degree.
5.degree. 5.degree. (5 + 2)s O.sub.2-plasma; flow-rate O.sub.2 200
ml/min, power 200 W III. Contact angle after 76.degree. 90.degree.
53.degree. 10.degree. 5.degree. 5.degree. (5 + 2)s CF.sub.4-plasma;
flow-rate CF.sub.4 200 ml/min, power 200 W; measured after
water-rinse Final film thickness (nm) 436 530 150 500 350 680
Example 2
Modification of Surface Properties by Silanisation with a
Fluoroalkylsilane
Preparation of Substrates
A Reference Substrate and Substrates 1-5 were Prepared as in
Example 1 above.
Plasma Treatment and Measurements
Substrates 1-5 and the Reference Substrate were rinsed with water.
Then the contact angles with water were measured for each of these
six substrates using a goniometer (contact angle measuring device)
with droplet size 1-5 .mu.l.
Subsequently, each of the six substrates was exposed to a CF.sub.4
plasma treatment in a Branson/IPC Series S2100 Plasma Stripper
system for 7 seconds at a flow rate of 200 ml/min and at a power of
200 W. Contact angles of the treated substrates were measured using
the same apparatus and methods as above. In the substrates with
high oxide content (B4 and B5), the inventors observed a fast
initial decrease of the contact angles, with the values slowly
stabilising after prolonged measurement times. Thus, the contact
angle ranges reported in table 3 below for the high oxide content
samples correspond to the initial values and the values obtained
after 5 minutes measuring time.
Subsequently, each of the six fluorinated substrates were exposed
to another CF.sub.4 plasma treatment in a Branson/IPC Series S2100
Plasma Stripper system for 7 seconds at a flow rate of 200 ml/min
and at a power of 200 W. Contact angles of the treated substrates
were measure using the same apparatus and methods as above. Again,
an initial decrease of the contact angles was observed for the
samples B4 and B5, with the values slowly stabilising after
prolonged measurement times. However, due to the higher initial
reaction rate after the second CF.sub.4 plasma treatment, the
initial contact angle values could not be determined accurately.
Therefore, only the contact angles determined after 5 minutes
measuring time are reported in table 3 below.
Subsequently, each of the six substrates was rinsed with de-ionised
water (Elix 10 DI water plant) and the contact angles with water
were measured again.
Finally, the rinsed substrates were treated with
(heptadecafluorodecyl)-trichlorosilane
(CF.sub.3(CF.sub.2).sub.7CH.sub.2CH.sub.2SiCl.sub.3) in an octane
solvent. The substrates were blown dry with nitrogen gas and then
their contact angles with water were measured again.
The resulting data is set out in table 3 below:
TABLE-US-00003 TABLE 3 Ref. B1 B2 B3 B4 B5 Vol. % (SiO.sub.2) in
film 0 17.3 29.5 38.6 44.9 50.4 Contact angle initial 75.degree.
91.degree. 93.degree. 118.degree. 133.degree. 133.degr- ee. (5 +
2)s 200 ml/min CF.sub.4/ 105.degree. 110.degree. 116.degree.
95.degree. 85.degree. 85.de- gree. 200 W to to 50.degree.
55.degree. (5 + 2)s 200 ml/min CF.sub.4/ 101.degree. 110.degree.
118.degree. 89.degree. 45.degree. 40.de- gree. 200 W Rinsing with
water 100.degree. 92.degree. 90.degree. 57.degree. 27.degree.
30.degree. Fluoro-SAM in octane 110.degree. 127.degree. 145.degree.
140.degree. 145.degree.
Data Analysis
From the above data, it can be seen that it is possible to create
highly hydrophilic and highly hydrophobic surfaces from substrates
which have silicon dioxide at their surface. Where a flexible
substrate precursor is used, these substrates would be flexible and
therefore useful in e.g. ink-jet printing processes as a part of
reel-to-reel processing. Thus it is possible to manufacture
flexible substrates comprising good wetting contrasts by carrying
out the methods 1-6 described above, as well as by other methods
known to the person skilled in the art, all of which make use of
substrates comprising an inorganic material at the surface. It is
noted that although these substrates have applicability in the
production of microelectronic devices by ink-jet printing, other
uses of the substrates can readily be envisaged where it is desired
to have a flexible substrate with a wetting contrast.
Best Mode
The best mode of the present invention is to prepare the substrate
using the fourth method of the present invention as described
above. This method allows the production of a flexible substrate
without the need for plasma treatment at any stage, which is
attractive because plasma treatment can only be carried out in a
vacuum chamber, which is not easily or cheaply installed.
Furthermore, the fourth method does not require a washing step, and
allows the production of a substrate comprising a wetting contrast
with only a few simple steps. The fourth method requires only the
steps of coating the substrate precursor with a solution of a
polymer and an inorganic material polymer, drying the coated
precursor to form the substrate, micro-embossing the substrate and
then exposing the un-embossed areas to a fluoroalkylsilane. All of
these steps are easily carried out in the context of reel-to-reel
processing. Preferably, the fourth method is carried out in the
following manner:
According to the fourth method, depicted schematically in FIG. 4, a
flexible substrate is prepared by coating a flexible, pre-treated
clear polyester substrate precursor (heat-stabilised, 125 .mu.m
thickness, 45.times.45 mm, from Coveme, Italy) with a PMMA solution
in butylacetate, the solution comprising 50 vol. % SiO.sub.2
particles (hexamethyldisilazane treated silica particles, 10-20 nm,
from ABCR) relative to the total amount of polymer and inorganic
particles, by spin-coating 1 ml of the solution onto the substrate
precursor for 30 seconds at 2000 rpm in air. The coated precursor
is then annealed for 12 minutes at 100.degree. C. in air to form
the substrate.
The substrate is then micro-embossed with a silicon mould for 20
minutes at 140.degree. C., 20 bar pressure, to form a patterned
area where the polymer layer is compressed. The surface is then
oxidised by atmospheric corona treatment to render the entire
surface hydrophilic. Heptadecafluorodecyl trichlorosilane is then
applied to the substrate surface (the non-embossed areas) with a
non-patterned polydimethylsiloxane (PDMS) soft stamp (Step D). This
renders the substrate surface hydrophobic and oleophobic, while the
embossed areas remain hydrophilic.
* * * * *